1. Field of the Invention
The present invention relates to driving circuitry of liquid crystal display. More particularly, the present invention relates to a voltage generator for a source driver of a liquid crystal display system.
2. Description of the Prior Art
A liquid crystal display (LCD) displays images by controlling transmittance of incident light emitted from a light source using optical anisotropy of liquid crystal molecules and polarization characteristics of a polarizer filter.
Each pixel of an LCD typically consists of a layer of molecules aligned between two electrodes. Voltages of managing and controlling of the data to be displayed is generated by driving circuits, one of which is often denoted as a gate driver while the other of which is denoted as a source driver. The source driver generates voltages of controlling the data to be displayed which will be applied to the two electrodes. These voltages control the transmittances of liquid crystal molecules to make pixels have different luminance so as to present an image.
In generally, the source driver requires a gamma reference voltage generator, which outputs a plurality of gamma reference voltages. The source driver utilizes these voltages to create different driving voltages to drive pixels. An example of a prior-art gamma reference voltage is depicted in FIG. 1. At first, a supply voltage VDDA provided by a power supply device is inputted to a resistor string. The resistor string produces a plurality of fractional parts of the supply voltage VDDA, VREF1-VREFN. The voltages VREF1-VREFN are provided to multiple DAC blocks to generate a plurality of gamma reference voltages VO1-VOM. The source driver will use these gamma reference voltages VO1-VOM to generate driving voltages for each pixel. Such a gamma reference voltage generator has two disadvantages: 1) noises due to poor power supply rejection ratio (PSRR) of the power supply device; 2) large size of the multiples DAC blocks.
Therefore, there is a need to provide an inventive voltage generator to address the above-mentioned problems.